The molecular-electronic mechanisms by which a protein environment modifies the properties of flavin coenzymes so as to generate a biochemically-specific enzyme system will be studied. The particular flavoproteins to be investigated are the flavodoxins and the photoreceptor pigment of Euglena. The approaches to be used with the flavodoxins include: chemical modification of amino acid side chains located in the coenzyme binding site; studies of the redox properties of flavin by hydroquinone, both free and protein-bound, as affected by complexation with amino acids and modifications of flavin structure; studies of protein flourescence; investigations of ionic strength and solvent dielectric effects on redox rates of free and bound flavins. The work with the Euglena photoreceptor will involve isolation, purification and characterization of the structural, spectral and photochemical properties of this material. This work has importance for an understanding of vitamin metabolism and nutrition, for enzyme mechanisms and for photocontrol of metabolic processes.